This invention concerns the manufacture of aryl esters having different substituents on the two aromatic rings.
The diphenylether derivatives, when substituted with functional groups, are industrial products of particular interest in the plastics industry; particularly, they take part in the manufacture of thermostable materials. Other functionalized compounds are intermediates for insecticides of very high efficiency.
Processes leading to the formation of an ether linkage between two aromatic rings are continuously researched with a view to improving their yield and/or selectivity.
It is known from Ullman's work that an alkali phenate reacts with a halogenated aromatic derivative to form an ether linkage. When the aromatic rings are unsubstituted or substituted with nonelectron attracting groups, the reaction requires severe conditions. When the reaction is effected with halogenated derivatives and aromatic phenates carrying electron attracting groups, the reaction is highly exothermic and difficult to control, especially when operating with large amounts of materials. In all cases these reactions require the use of two different compounds, the phenate and the halogenated derivative.
German Pat. No. 1 290 148 and No. 2 104 201 describe a new reaction for the production of diphenylethers substituted with electron attracting groups; the results of these works have been again published by H. Witt, G. Holtschmidt and E. Muller (Angew. Chem. Internat. Edit. 9, 1970 (1) p. 67). The process is based on the thermal decomposition with base catalysis of the corresponding phenyl carbonates. This process has the advantage of making use of a single starting product, the substituted phenol, and of making it possible to follow the course of the extent of reaction, which occurs in bulk, by the carbon dioxide evolution.
This process is particularly adapted to the synthesis of diphenylethers substituted on each phenyl ring with identical electron attracting groups such as CN, NO.sub.2, carboxylic ester or phenylsulfone, but it does not solve the problem of synthesizing diphenylether derivatives substituted with two different electron attracting groups and these products may constitute highly desirable raw materials for manufacturing plastic materials.